Process for coating paper



Dec. 19, 1950 -w. H. BARRETT EI'AL PROCESS FOR COATING PAPER Original Filed Odt. 28, 1944 Inventors: \nl. H.Bc1rrztt B. KAsdeLL i atented Dec. 19, 1950 PROCESS FOR COATING PAPER William H. Barrett, international Falls, Minn and Bernard K. Asdell, Metuchen, N. 3., assignors to Minnesota and Ontario Paper Company,

Minneapolis, Minn.

Original application October 28, 1944, Serial No.

569,358. ilh ided and this application Novemher 15, 1946, Serial No. 769,936

2 Claims. 1

This. invention relates to the art of coating and generally to the art of coating web material, and has reference more particularly to webs of paper which can be processed in a continuous manner while moving at high rates of speed.

One of the objects of the invention is to provide an apparatus and a process of coating web material. by which two. coats of uniform and continuous film of coating material may be applied to the same side of the web in a predetermined arrangement for insuring uniform products and large quantity production.

Another object of the invention is to provide a uniform thickness and a coating material which is durable and flexible which does not extend substantially into the structure of the paper.

The thickness of the coating on the paper or sheet material is extremely important both to the manufacturer and the user. Where the coating is for moisture proofing purposes, a coating of constant thickness will provide a finished Web or sheet of known moisture proofness. For the manufacturer a variation of coating thicknesses presents more serious problems. In the first in stance, a variation of thickness of the coating varies the drying time of the coated sheet. Thus, if the drier is set to dry the coating of a certain thickness, certain portions of the sheet which are lightly coated might be dried to too great an extent with a bad effect on the finished product. Other parts of the coated sheet might bear a coating of excessive thickness which might not be perfectly dry during the travel of the web or sheet, thus producing a product which is not uniform in grade.

It is often desirable to place a coating film of greater than ten pounds per ream of 25 x 28/500 sheets on one side of the sheet of paper. One of the difficulties in applying such a heavy coating is that the coating tends to crawl or in other words, form an uneven surface. It has been discovered that if the heavy coating is applied in two or more applications, the difliculties of pro ducing an uneven finished surface is avoided.

Other objects and advantages of the present in- Vention will be apparent from the accompanying drawings, and the following detailed description:

In the drawing forming a part of the specification, similar reference characters indicate corresponding parts in all the views. Figure 1 is a side elevational view of a coating apparatus for carrying out the process hereinafter described; Figure 2 is a sectional view with parts broken away of the top doctoring roll; Figure 3 is a sectional view of the felt with a coated sheet (Cl. 117-11l) q a of paper thereon. and Fig. 4 shows arrangement of the coating rolls and their direction of. rotation.

Referring to the drawing in detail: It indicates a roll of raw stock or paper which is to be v coated, means [2 is for controlling the tension on. the paper from the unwinding roll it. A motor It. for driving the coating apparatus is provided and the motor drives the apparatus through membersl i, l5 and it. The web ll as it is unwound from the roll, passes over roll i3 which is sup.- ported by arms i9 and tension is maintained on the rolls :8 by spring 20 which is attached to the frame 23- at 22' and to the arm IE3 at 21. The frame for supporting the coating unit consists of upright member 23, horizontal members 24., 25. 26 and 28.

The web of paper after passing over roll 18 passes around roll 29 whichv is suitably secured in bearings 56. The web of paper then passes between tensioning rolls 3!. and 35: which: are suitably supported by bearings $2 and 34. The web of paper after passing between rolls 3i and 33 pass. over roll 35 and then under roll 3t. Roll 36 is mounted so that tension is maintained on the paper through the medium of arms 31' which are pivoted at point 38. The paper then passes over roll 35 which is mounted. in bearings Ml. This roll and itsv bearings are mounted on member 26 and may be adjusted on frame mem ber 26 to a desired position. The paper then comes into contact with drier drum or backing member 44 which is mounted upon shaft 45:. The shaft $5 is suitably sup-ported by upright member 46. Associated with the drier drum is felt 41 which is used for the purpose of eliminating drier wrinkles. The felt All leaves the surface of the drier and then passes over roll. 48 which is suitably mounted in bearings 45. The felt then travels with the paper over rolls 58 and 52 which rolls are respectively mounted-in bearings 5! and 53. The felt then passes around roll 54 which is mounted in bearings 55. The felt then passes to the felt guide which consists of. an arm 56 and felt edge contacting means 5?. The arm 56 is associated with movable roll 58 and arm 56 and roll 58 are secured to member The purpose of the felt guide is to aid in maintaining the felt in position on the drier drum M2 The felt then passes over roll 6% mounted in suitable bearings 5| and then surrounds rolls 62and 54, back into contact with the drier surface. The rolls 62 and 54 are mounted in bearings 53 and 65 which may be moved along the frame members 25 and 23 so as to vary the contacting of the felt with the drier surface. The paper after passing over the roll 52 passes in contact with roll 66 mounted in suitable bearings 67 and then to the wind-up stand. The wind-up stand consists of rolls 88 and 69 arranged to be driven at the same speed by belt-like member ID. The roll T5 indicates the coated paper being wound up. The purpose of the roll 12 is to prevent excessive movement of the roll of paper during a wind up.

The coating unit consists of a fountain 14 in which is mounted metering roll 15. The roll 15 is mounted in bearing 16 which is supported by arm 11 which is pivoted at 18 so that the hard surfaced metering roll 15 and the fountain can be moved away from the applicator roll 83. Positioned below the fountain I4 is coating supply tank 19. The coating from the fountain '14 fiows over the back of the fountain 14 into the supply tank 19. The supply tank 19 is furnished with a coating material from a suitable source not shown. The coating material is withdrawn from the coating container 19 through pipe 89 by pump 8| and forced through pipe 82 into the fountain near the top thereof. Rotating into one side of the fountain is roll 83 which is mounted on suitable bearings 84. Positioned above the roll 83 in suitable bearings 86 is hard surfaced doctor roll 85. The doctor roll 85 is preferably hard surfaced material such as stainless steel, while the applicator roll 83 is preferably of a yieldabie Positioned in contact transfers one coat of the coating material to the paper. Positioned above roll 81 is hard surfaced roll 98 for doctoring the surplus coating from the surface of the applicator roll 81. This doctoring roll is wiped clean by a resilient surfaced roil 9| mounted in bearings 92. Bearings 92 are supported by member 93 while roll 81 is supported by arm member 94 and the applicator roll 83 is supported by arm member 95a. The arm 95 is pivotally connected to member 95a which mem her in turn is pivotally connected at 94a so that the applicator roll and the doctor rolls can be moved toward and from the backing roll or drier surface. The arms 93, 94 and 95 are pivotally connected to upright member 91 at 88, 99 and 98. The upright member 91 is pivotally connected at lfll so that the coating and doctoring rolls may be moved (through any desired means not shown) away from and toward the drier or backing member to provide means for varying the pressure between the doctoring rolls and applicator rolls. A member I02 is connected to arm 93 at 183 and to member 185 at 504. An eccentric IDS is positioned in arm 94 and connected to member 82.

The eccentric is provided with a handie 8? for varying the pressure between the rolls 83, 85, 3? and 9!. Member E85 is connected to member I02 at I84 and to member 95 to control the amount of coating material on applicator roll 83. An eccentric iEfia is connected to the frame member carrying the metering roll i5 through member We. The eccentric lBSa has connected therewith handle member 16141. To remove the coating material from the surface of the doctoring roll 9|, doctor blade I89 is adjustably positioned against the surface. This doctoring blade is suitably supported by member :88. The surplus coating material removed from the roll 9! is returned through trough Ill and pipe H2 to the coating container 19.

In operation, the coating material is fed to the fountain I4 and an excess of coating material is forced between the applicator roll 83 and the metering roll 15. A predetermined amount of coating material is left upon the surface of the roll 83 by the metering roll 15 which breaks up any ridges in the coating film. The coating on the rubber surfaced roll flows or distributes into a smooth film particularly adjacent the roll surface. The doctor roll 85 removes a predetermined amount from the applicator roll 83 and the remainder of the coating on the applicator roll after it has been smoothed and the surplus removed by roll 85 is applied to the web of paper which is supported by the backing roll 44 in a smooth and even film across the width of the web. The coating material now on the surface of the doctoring roll 85 is transferred to the surface of the applicator roll 8'1. The coating material on the applicator roll 81 is then smoothed and the surplus removed therefrom by doctor roll 98. The coating material removed from the surface of the applicator roll 87 is then transferred to the surface of the web of paper which is supported by the backing roll 44. The coating material removed by the doctor roll 90 is removed by resilient covered doctor roll 9| and then the doctor blade removes the coating material from the doctor roll 9i and the coating is returned to the coating container. The foregoing may be accomplished by having drier roll 44, metering roll 15, applicator roll 83, doctor roll 85, applicator roll 8?, doctor roll 90 and resilient covered doctor roll 9! rotate in the direction shown in Figure 4, it being understood that the roll may be driven by any suitable means (not shown).

The paper to be coated preferably contains a moisture content of not more than about ten percent at the time the first coat of coating ma terial is applied, and the coating material used preferably should have a solid content of greater than sixty percent. The apparatus and the process hereinhefore described may be used with hot melt coating material, and in such a case the backing member or roll 44 is provided with a cooling medium. Where the coating is of the mineral-adhesive such as starch clay or similar material, the backing means is preferably heated to dry the coating material applied to the paper.

Various changes from the detailed description and specific steps of the process will occur to those skilled in the art without departing from the spirit of the invention or the scope of the appended claims.

Another feature of this invention is the application of a wet film of coating material over another wet film of coating material. This is termed wet trapping. For the purpose of this application, wet trapping is defined as the application of a wet film of coating material over another wet film. It is possible in this application I to Wet trap without changing the viscosity of the coating material.

plying surface, removing a portion of the coatin so applied and smoothing the remainder to a smooth film on the second applying surface, applying the removed portion of the coating composition to a first rotatable applying surface and smoothing the coating to a smooth film, transferring the smooth film of coating on the first rotatable applying surface to the heated moving web of paper, and then applying the smooth film on the second rotatable applying surface over the film applied to the moving web of paper while the film of coating material applied to the paper is still wet.

2. The process of applying smooth films of coating composition having a solid content in excess of 60% to a moving web of paper containing moisture of less than about 10% comprising the steps of bringing the moving web of paper into heat exchange with a rotatable heated surface, applying the high solid coating composition to a rotatable applying surface, smoothing the coating on the rotatable applying surface to a smooth film and removing a portion of the coating composition applied, applying the re- WILLIAM H. BARRETT. BERNARD K. ASDELL.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,983,690 Behrens Dec. 11, 1934 2,093,347 Beecher Sept. 14, 1937 2,293,690 Harrigan Aug. 18, 1942 2,369,378 Thiele, et al. Feb. 13, 1945 2,416,789 Barrett et al Mar. 4, 1947 

1. A PROCESS OF COATING ONE SIDE OF A MOVING WEB OF PAPER HAVING A MOISTURE CONTENT OF LESS THAN ABOUT 10% WITH TWO SMOOTH FILMS OF MINERAL ADHESIVE COATING COMPOSITION HAVING A SOLID CONTENTS IN EXCESS OF 60% COMPRISING HEATING A MOVING WEB OF PAPER PRIOR TO THE APPLICATION OF COATING COMPOSITION THERETO, APPLYING AN EXCESS OF COATING COMPOSITION TO A SECOND ROTATABLE APPLYING SURFACE, REMOVING A PORTION OF THE COATING SO APPLIED AND SMOOTHING THE REMAINDER TO A SMOOTH FILM ON THE SECOND APPLYING SURFACE, APPLYING THE REMOVED PORTION OF THE COATING COMPOSITION TO A FIRST ROTATABLE APPLYING SURFACE AND SMOOTHING THE COATING TO A SMOOTH FILM, TRANSFERRING THE SMOOTH FILM OF COATING ON THE FIRST ROTATABLE APPLYLING SURFACE TO THE HEATED MOVING WEB OF PAPER, AND THEN APPLYING THE SMOOTH FILM ON THE SECOND ROTATABLE APPLYING SURFACE OVER THE FILM APPLIED TO THE MOVING WEB OF PAPER WHILE THE FILM OF COATING MATERIAL APPLIED TO THE PAPER IS STILL WET. 